1. Field of the Invention
The present invention pertains to graphic displays and, more particularly, to conformable true color graphic displays fully visible in both front and back light.
2. Discussion of the Prior Art
Color graphics for daylight or front lighting applications are created by layering pigment inks on opaque white substrate. Color graphics for dramatic nighttime back lighting are produced by applying pigment inks to translucent substrate. Front lighting produces images that result from light that passes through the ink, is reflected by the opaque substrate and passes back through the ink to the observer, while back lighting images result from light that passes through the translucent substrate, then through the ink and on to the observer. As a result, front lighting images transit the inked layer twice and back lighting images transit the inked layer once so that back lit graphics must be considerably more heavily pigmented in order to obtain the same spectral content or color fidelity as front lit graphic displays. Consequently graphics capable of faithfully producing back lit colors appear dark and inaccurate when viewed by front light. Advertising frequently demands exact colors in all viewing situations, especially where logos are characterized as much by color as by shape, and the color distortion associated with daylight viewing of traditionally produced back lighting graphics is not acceptable. In addition, the mechanics of providing uniform fluorescent or incandescent light for even moderately sized back lit color graphics has been discouragingly difficult, costly and space consuming. Advertisers have been faced with the choice between accepting the seriously degraded visual presentation prior art back lighting produces in daylight or forfeiting the desirable eye catching effects they produce at night.
The moving billboard advertising opportunity presented by the sides of cargo trailers is illustrative of the prior art dilemma. Vivid commercial art generally adorns the daylight observation of these prime advertising surfaces, but after dark the value of the space is lost or compromised by typically weak and unpredictable front lighting from external sources or side lighting attached to the truck trailer. Protruding front lighting schemes mounted to the truck present the added disadvantage of being damaged when the trailer is being moved in the close spaces typical of loading terminals, and adds to wind resistance, thereby increasing fuel consumption and cost.
A new method for producing color graphics presenting essentially the same spectral content when illuminated by front lighting or by back lighting, a quality termed "transflectivity", has been disclosed and claimed in U.S. Pat. No. 5,144,328 (Blake et al), and is incorporated herein by reference. In this process nearly identical graphic images are inked onto each side of a translucent substrate in full registry, that is, in complete alignment with each other. Daylight or front lighting passes through the inked image on the front side of the substrate, and is reflected by the substrate back through the image to the viewer, passing through the front ink image twice. Back lighting the same graphic results in light passing through the inked image on the back side of the substrate, through the substrate, then through the image on the front side and on to the viewer, resulting in two passages through two identical ink images. The viewer is presented in each case with an image produced by light having been acted upon by two thicknesses of ink and thus the same spectral content or, color fidelity, is achieved by both lighting arrangements. Where substantial differences exist in the spectral content of the front light source and the back light source, compensations can be made in the pigmentation concentrations used on the back surface without altering the colors viewed with front lighting.
Advances in electroluminescent technology have resulted in the development of efficient flexible planar lamps having finely divided electroluminescent phosphor embedded in a layer of light transmitting resin bonded between a non-transparent electrode layer and a substantially transparent electrode layer. An example of such a lamp is disclosed and claimed in U.S. Pat. No. 4,020,389 (Dickson et al), incorporated herein by reference. Such lamps can be fabricated into large thin sheets having a bending radius on the order of 0.5 inches for a 180.degree. turn, capable of being cut into a variety of shapes and sealable against weather effects. The lamps produce light of uniform intensity in the 7 to 25 foot-lamberts per square inch range over the entire surface and require modest levels of alternating current.
U.S. Pat. No. 4,138,620 (Dickson) teaches overlapping electroluminescent panels on a relatively stiff support plate within an aluminum frame to provide large areas of uniform illumination, overlaying such panels with fluorescent pigment graphics, and maintaining registration or alignment between the graphics and the electrolumenescent panels. These panels are relatively heavy, are difficult to mount and install and increase vehicle wind resistance; accordingly, they have not found commercial acceptance for vehicle advertising applications.
There exists in the prior art a long felt need for practical true color day-night graphic displays commercially suitable for use on irregularly contoured and soft-sided vehicle sides and ends.